The Role of Genetics in Ankylosing Spondylitis
Ankylosing spondylitis (AS) is type of chronic inflammatory arthritis that affects the spine but has no known cause. Doctors do suspect for many people the disease is genetic.
Those with AS have an abnormality in their DNA, a molecule that contains your unique genetic code, which contributes to the development of the disease.
Who Gets Ankylosing Spondylitis?
Anyone can develop AS. It most often begins in the late teen years or early adulthood and is more common among men, Caucasians and in families with a history of AS. Up to 1.4% of Americans have ankylosing spondylitis —that’s almost 4 and a half million people.
Ankylosing Spondylitis in the United States
There are about 60 genes researchers think may be connected to AS and similar inflammatory diseases. The way our population is spread across the globe, genetic diseases often have unique gene abnormalities found in different parts of the world. This results in certain genetic changes being more prevalent in some areas than others. For example, 7% of people in the general population of the U.S. have a genetic abnormality called the HLA B27 gene. What is particularly interesting to researchers is 90% of people with AS in the U.S. also have that gene. So while having the HLA B27 gene doesn’t mean you will definitely develop AS, if you do have the HLA B27 gene, it’s estimated you have a 5% to 6% chance of developing it. But, if you have been diagnosed with AS, there is a very high chance that you do carry this gene.
What the HLA B27 Gene Does
The HLA B27 gene produces a protein which is harmless in most people. But for some, the protein plays a role in immune system dysfunction, causing inflammatory diseases such as AS and psoriatic arthritis. Researchers don’t know exactly how yet.
Testing for the HLA B27 Gene
There is a blood test that indicates if you carry the HLA B27 gene. It’s generally performed if there’s a suspicion of AS or a related illness. A negative finding for the gene means you don’t have AS. If you don’t have it, it will not develop. A positive finding, which means the gene is present, is one clue to a possible diagnosis of AS, to be used in combination with other information, such as your medical history, and signs and symptoms.
Treatments for AS
Current treatment for AS focuses on managing symptoms and preventing progression of the disease. This includes medication to relieve pain and inflammation, physical therapy and in some cases, surgery. At this time there’s no treatment for AS related specifically to the HLA B27 gene, although there are studies investigating immunotherapy, a type of treatment that uses your own immune system to fight certain diseases and infections, to help block the protein’s effect on the body’s inflammation.
Should HLA B27 Be a Screening Test?
Given that 90% of people in the U.S. who have AS do have the HLA B27 gene, some people may wonder if there should be screening tests to look for the gene. This is not done routinely because so many people have the gene but don’t go on to develop the disease. Such a screening test wouldn’t be useful in this case. That being said, if you have a first-degree relative (parent or sibling) who does have AS, speak with your doctor about being tested. However, it’s important to keep in mind that not having the gene doesn’t guarantee that you won’t get the disease, since 10% of people in the U.S. with AS don’t have HLA B27 either.
We can’t yet prevent diseases like AS even if you know you have the HLA B27 gene. But if AS runs in your family, knowing you may be at higher risk of developing the disease could help you prepare for it and to recognize the signs and symptoms, allowing for earlier treatment. Earlier treatment could help slow down or minimize damage to your spine and joints.